Create Block Theme: Theme tags are incorrectly capitalized when saving a theme

Problem

When saving a theme using the Create Block Theme plugin, some WordPress theme tags are output with capitalized letters — for example Blog, Block-Styles, RTL-Language-Support — instead of the correct lowercase, hyphenated format (blog, block-styles, rtl-language-support). This causes the tags to be invalid or unrecognized in the WordPress theme directory, and fails the formatting conventions expected in style.css theme headers.

Steps to Reproduce

• Set up a theme with tags via the Create Block Theme interface
• Add more tags to the theme through the style.css file
• Save the theme using Create Block Theme
• Check style.css and inspect the tags
• Note incorrectly capitalized tag values (e.g., blog becomes Blog).

Expected Behavior

All theme tags are written in lowercase with hyphens, matching the WordPress theme directory format — e.g. blog, block-styles, rtl-language-support, threaded-comments, translation-ready.

Actual Behavior

Some or all tags are capitalized or inconsistently cased in the output.

Environment

Plugin: Create Block Theme
File affected: style.css (theme header)

Start by inspecting the theme-saving path that writes the style.css theme header, using the reported capitalization examples as reproduction cases. Confirm the saved tags use lowercase letters and hyphens, including blog, block-styles, rtl-language-support, threaded-comments, and translation-ready.